Spread spectrum communication system and transmitter-receiver

ABSTRACT

A spread spectrum communication system for performing spread spectrum communication by superimposing a pseudo noise signal on a transmitted signal. The system comprises traffic detecting means for detecting the traffic of the transmitted signal, and means for changing the clock frequency of the pseudo noise signal in accordance with the output from the traffic detecting means. The system may alternatively comprise transmission quality determining means for determining the transmission quality of the received signal, and means for changing the clock frequency of the pseudo noise signal in accordance with the transmission quality determined by the transmission quality determining means. In operation, the system offers improved S/N ratios where traffic is high or transmission quality is low, saves power where traffic is low or transmission quality is high and ensures large margins of power control precision for mobile stations near the upper limit of the system&#39;s line capacity.

This is a divisional of application Ser. No. 07/942,708 filed on Sep. 9,1992, now U.S. Pat. No. 5,321,721 which is hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a spread spectrum communication systemand a transmitter-receiver based on CDMA (code division multiple access)and, more particularly, to a spread spectrum communication system and atransmitter-receiver capable of adaptively changing the power level oftransmitted signals.

2. Description of the Related Art

The spread spectrum communication system works in principle as follows:The transmitter of the system modulates (spreads) by pseudo noise (PN) acarrier that carries data. The receiver subjects the received carrier toa PN-coded correlation (reverse spread) process, the PN being generatedby an encoder structurally identical to the one used by the transmitter.The PN-code correlation process is followed by base band demodulationthat restores the transmitted data. Under this spread spectrumcommunication scheme, the density of power per unit frequency is low.This means that a minor increase in noise level accompanying a highertraffic, insignificant For other kinds of communication, can lead to adegenerated S/N (signal-to-noise) ratio with the spread spectrumcommunication system. The raised noise level hampers efforts tocommunicate using a desired signal under the spread spectrumcommunication scheme.

One prior art solution to the above problem is to widen the frequencyband of spread spectrum signals while lowering the power density perunit frequency. This requires enhancing the clock rate of thetransmitter, which means greater power dissipation. In that case, evenif traffic is low, the clock rate remains unnecessarily high reflectingthe increased power consumption.

FIG. 1 is a block diagram of a modulating portion in a transmitter foruse with a conventional direct spread spectrum communication system. InFIG. 1, a carrier generator 201 generates a carrier fc for input to aPSK (phase shift keying) modulator 202. The PSK modulator 202 subjectsthe carrier fc to bi-phase shift keying modulation using a transmittedsignal (binary coded signal) d(t) from an input terminal 203. ThePSK-modulated signal from the PSK modulator 202 is supplied to a spreadspectrum modulator 204. The spread spectrum modulator 204 is fed with aspread signal p(t) from a PN generator 205 that generates a PN (pseudonoise) code sequence. Using the spread signal p(t), the modulator 204subjects the PSK-modulated signal to spread spectrum modulation.

FIG. 2A is a view of a typical change in the transmitted signal d(t)used by the modulation portion of FIG. 1. FIG. 2B is a view of afrequency spectrum of the PSK-modulated signal output by the PSKmodulator 202 in FIG. 1. In FIG. 2A, Td is the period of the transmittedsignal d(t). The frequency band width Bd is given as

Bd=1/Td

FIG. 3A is a view of a typical change in the spread signal p(t) from thePN generator 205. FIG. 3B is a view of a frequency spectrum of thespread spectrum signal output by the spread spectrum modulator 204. InFIG. 3A, Tp is the period of the spread signal p(t). As shown in FIGS.3A and 3B, the period Tp of the spread signal p(t) changes last overshort time with respect to the period Td of the transmitted signal d(t).This causes the spread spectrum modulator 204 to spread the frequencyspectrum over a wide band (frequency band width Bp=1/Tp).

FIG. 4 is a block diagram of a demodulating portion of a receiver foruse with the direct spread spectrum communication system of FIG. 1. InFIG. 4, the spread spectrum signal received by an antenna of the like,not shown, and admitted through a terminal 211 enters a band-pass filter(BPF) 212. The band-pass filter 212 retains only those components of thesignal which constitute the necessary band and discards the rest.

Past the band-pass filter 212, the spread spectrum signal goes into areverse spread device 213 illustratively made of a multiplier. For itsreverse spread operation, the reverse spread device 213 is fed by a PN(pseudo noise) generator 214 with a signal p(t)' identical to theabove-mentioned spread signal p(t). In this case, the signal p(t)' fromthe PN generator 214 is so controlled as to coincide in phase with thespread signal p(t). That is, the relation

    p(t)·p(t)'=p(t).sup.2 =1

should hold.

The output signal from the reverse spread device 213 goes to a band-passfilter 215 whose center frequency is fc and whose passing band is 2Bd.The band-pass filter 215 extracts a PSK-modulated signal from the signalreceived. The PSK-modulated signal is supplied to and demodulated by aPSK demodulator 216. As a result, the original signal d(t) is tappedfrom an output terminal 217. Spread spectrum communication, as outlined,is a communication method whereby a frequency spectrum is spread over awide band for communications that ensure security and privacy with highimmunity to interference.

To keep the spread spectrum communication system normally operationalrequires conventionally that the receiving power of the base stationremain constant over the communication channels connected to subordinatemobile stations. It is thus necessary to keep constant the transmittingpower of each mobile station as it communicates with the base stationwhile moving under varying external conditions. Theoretical calculationsput the precision of transmitting power control to within 0.5 dB in thevicinity of the upper limit of the system's circuit capacity. Inpractice, that kind of precision is difficult to achieve. This has beena major problem with spread spectrum communication systems based on CDMA(code division multiple access).

FIG. 5A is a view of a frequency spectrum of the signal sent from theinput terminal 211 to the band-pass filter 212 in FIG. 4. FIG. 5B is aview of a frequency spectrum of the signal sent from the reverse spreaddevice 213 to the band-pass filter 215 in FIG. 4. FIG. 5C is a view of afrequency spectrum of the signal sent from the band-pass filter 215 tothe PSK demodulator 216 in FIG. 4. In FIG. 5A, the spread spectrumsignal with a band width of 2Bp mixes with a narrow band interferencecomponent. If the power of the signal in FIG. 5A is denoted by Pr andthat of the interference wave by P_(I), the signal-to-interference wavepower ratio (S/I)_(A) is given as

(S/I)_(A) =Pr/P_(I)

In FIG. 5B, a reverse relationship of what is given in FIG. 5A holds.That is, the signal passes through the band-pass filter 215 having aband width of 2Bd. The result is shown in FIG. 5C. In this case, thesignal-to-interference wave power ratio (S/I)_(C) is given as ##EQU1##where, G stands for a process gain (G=Bp/Bd). As indicated, subjectingthe input signal to spread spectrum modulation improves thesignal-to-interference wave power ratio From (S/I)_(A) to (S/I)_(C),i.e., by the amount of G. Thus the spread spectrum communication schemeenhances the immunity to the adverse effects of interference signalcomponents.

Consider the case where white noise is involved, with no narrow bandinterference signal component present. In this case, as above, thespectrum patterns of the respective signals in FIG. 4 appear as depictedin FIGS. 6A, 6B and 6C. The signal-to-noise ratio (S/N)_(A) of thesignal FIG. 6A is given as

    (S/N).sub.A =Pr/(No·2Bp)

where, No is the power of the white noise signal component. Likewise,the signal-to-noise ratio (S/N)_(C) of the signal in FIG. 6C is given as##EQU2## The case above thus yields the same result as that of the casewhere the narrow band interference signal component is involved asdepicted in FIG. 5.

In the case of communication within one system whose terminals utilizethe same PN code, a given terminal regards the communication done by anyother terminal as a noise similar to the white noise. That is, when oneterminal transmits its signal at a raised power level, the terminal notonly dissipates more power than before but also interferes with thecommunication of other terminals. Communication carried out underschemes other than the spread spectrum communication constitutes acomponent approximating the narrow band interference signal component.In any case, higher levels of traffic lead to the increase in the noiseindicated by the shaded portions in FIGS. 5C and 6C. This is asignificant impediment to the normal execution of communication.

One prior art solution to the above impediment is to enlarge the bandwidth Bp off the spread spectrum signal so as to increase the processgain G. This requires boosting the clock rate for reverse spreadoperation through multiplication of the spread signal p(t)' in FIG. 4.The solution results in more power dissipation of which the level turnsout to be disproportionately high where the process gain G need not bevery high.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a spreadspectrum communication system and a transmitter-receiver which offerimproved S/N ratios where traffic is high or transmission quality islow, and which save power where traffic is low or transmission qualityis high.

It is another object of the invention to provide a spread spectrumcommunication system and a transmitter-receiver which ensure largemargins of power control precision for mobile stations in the vicinityof the upper limit of the system's line capacity.

It is a further object of the invention to provide a spread spectrumcommunication system and a transmitter-receiver which keep thetransmitting power involved at appropriate levels.

In carrying out the invention and according to a first aspect thereof,there is provided a spread spectrum communication system for performingspread spectrum communication by superimposing a pseudo noise signal ona transmitted signal, the spread spectrum communication systemcomprising: traffic detecting means for detecting the traffic of thetransmitted signal; and means for changing the clock frequency of thepseudo noise signal in accordance with the output from the trafficdetecting means.

According to a second aspect of the invention, there is provided aspread spectrum communication system for performing spread spectrumcommunication by superimposing a pseudo noise signal on a transmittedsignal, the spread spectrum communication system comprising:transmission quality determining means for determining the transmissionquality of a received signal; and means for changing the clock frequencyof the pseudo noise signal in accordance with the transmission qualitydetermined by the transmission quality determining means.

According to a third aspect of the invention, there is provided a spreadspectrum transmitter-receiver for superimposing a pseudo noise signal ona transmitted signal and for receiving the transmitted signal containingthe superimposed pseudo noise signal, the spread spectrumtransmitter-receiver comprising: transmission quality determining meansfor determining the transmission quality of a received signal; means forcontrolling the clock rate of the pseudo noise signal in accordance withthe transmission quality determined by the transmission qualitydetermining means; and means for combining information about the changedclock rate with the transmitted signal.

According to a fourth aspect of the invention, there is provided aspread spectrum transmitter-receiver for superimposing a pseudo noisesignal on a transmitted signal and for receiving the transmitted signalcontaining the superimposed pseudo noise signal, the spread spectrumtransmitter-receiver comprising: traffic detecting means for detectingthe traffic of the transmitted signal; means for controlling the clockrate of the pseudo noise signal in accordance with the output from thetraffic detecting means; and means for combining information about thechanged clock rate with the transmitted signal.

According to a fifth aspect of the invention, there is provided a spreadspectrum transmitter-receiver comprising: transmission qualitydetermining means for determining the quality of a received signal fromthe other spread spectrum transmitter-receiver; control data generatingmeans for generating clock control data for controlling the clock rateof a pseudo noise signal from the other spread spectrumtransmitter-receiver in accordance with the transmission qualitydetermined by the transmission quality determining means; data combiningmeans for combining with a transmitted signal the clock control datagenerated by the control data generating means; and a band-pass filtercircuit for controlling a passing band in accordance with the changedclock rate of the pseudo noise signal in the received signal from theother spread spectrum transmitter-receiver.

According to a sixth aspect of the invention, there is provided a spreadspectrum transmitter-receiver comprising: traffic detecting means fordetecting the traffic of a received signal from the other spreadspectrum transmitter-receiver; control data generating means forgenerating clock control data for controlling the clock rate of a pseudonoise signal from the other spread spectrum transmitter-receiver inaccordance with the output from the traffic detecting means; datacombining means for combining with a transmitted signal the clockcontrol data generated by the control data generating means; and aband-pass filter circuit for controlling a passing band in accordancewith the changed clock rate of the pseudo noise signal in the receivedsignal from the other spread spectrum transmitter-receiver.

According to a seventh aspect of the invention, there is provided aspread spectrum transmitter-receiver system comprising: a second spreadspectrum transmitter-receiver having transmission quality determiningmeans for determining the transmission quality of a received signal froma first spread spectrum transmitter-receiver, control data generatingmeans for generating clock control data for controlling the clock rateof a pseudo noise signal from the first spread spectrumtransmitter-receiver in accordance with the transmission qualitydetermined by the transmission quality determining means, and datacombining means for combining with a transmitted signal the clockcontrol data generated by the control data generating means; and thefirst spread spectrum transmitter-receiver having data extracting meansfor extracting the clock control data from a received signal from thesecond spread spectrum transmitter-receiver, and clock control means forcontrolling the clock rate of the pseudo noise signal in accordance withthe clock control data extracted by the data extracting means.

According to an eighth aspect of the invention, there is provided aspread spectrum transmitter-receiver system comprising: a second spreadspectrum transmitter-receiver having traffic detecting means fordetecting the traffic of a received signal from a first spread spectrumtransmitter-receiver, control data generating means for generating clockcontrol data for controlling the clock rate of a pseudo noise signalfrom the first spread spectrum transmitter-receiver in accordance withthe output from the traffic detecting means, and data combining meansfor combining with a transmitted signal the clock control data generatedby the control data generating means; and the first spread spectrumtransmitter-receiver having data extracting means for extracting theclock control data from a received signal from the second spreadspectrum transmitter-receiver, and clock control means for controllingthe clock rate of the pseudo noise signal in accordance with the clockcontrol data extracted by the data extracting means.

According to a ninth aspect of the invention, there is provided a spreadspectrum communication system for performing spread spectrumcommunication by superimposing a pseudo noise signal on a transmittedsignal, the spread spectrum communication system comprising: trafficdetecting means for detecting the traffic of the transmitted signal; andmeans for changing the clock frequency of the transmitted signal inaccordance with the output from the traffic detecting means.

According to a tenth aspect of the invention, there is provided a spreadspectrum communication system for performing spread spectrumcommunication by superimposing a pseudo noise signal on a transmittedsignal, the spread spectrum communication system comprising:transmission quality determining means for determining the transmissionquality of a received signal; and means for changing the clock frequencyof the transmitted signal in accordance with the transmission qualitydetermined by the transmission quality determining means.

According to an eleventh aspect of the invention, there is provided aspread spectrum transmitter-receiver for superimposing a pseudo noisesignal on a transmitted signal and for receiving the transmitted signalcontaining the superimposed pseudo noise signal, the spread spectrumtransmitter-receiver comprising: transmission quality determining meansfor determining the transmission quality of a received signal; means forcontrolling the clock rate of the transmitted signal in accordance withthe transmission quality determined by the transmission qualitydetermining means; and means for combining information about the changedclock rate with the transmitted signal.

According to a twelfth aspect of the invention, there is provided aspread spectrum transmitter-receiver for superimposing a pseudo noisesignal on a transmitted signal and for receiving the transmitted signalcontaining the superimposed pseudo noise signal, the spread spectrumtransmitter-receiver comprising: traffic detecting means for detectingthe traffic of the transmitted signal; means for controlling the clockrate of the transmitted signal in accordance with the output from thetraffic detecting means; and means for combining information about thechanged clock rate with the transmitted signal.

According to a thirteenth aspect of the invention, there is provided aspread spectrum transmitter-receiver system comprising: a first spreadspectrum transmitter-receiver having transmission quality determiningmeans for determining the transmission quality of a received signal,control data generating means for generating clock control data forcontrolling the clock rate of a transmitted signal in accordance withthe transmission quality determined by the transmission qualitydetermining means, and data combining means for combining with thetransmitted signal the clock control data generated by the control datagenerating means; and a second spread spectrum transmitter-receiverhaving data extracting means for extracting the clock control data fromthe received signal, and clock control means for controlling the clockrate of the transmitted signal in accordance with the clock control dataextracted by the data extracting means.

According to a fourteenth aspect of the invention, there is provided atransmitter-receiver comprising: loss estimating means for estimatinglosses over a propagation path in accordance with a received signal; andpower control means for controlling transmitting power in accordancewith the result of estimation by the loss estimating means.

The above and other objects, features and advantages of the presentinvention and the manner of realizing them will become more apparent,and the invention itself will best be understood from a study of thefollowing description and appended claims with reference to the attacheddrawings showing some preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a modulating portion in a transmitter foruse with a conventional direct spread spectrum communication system;

FIG. 2A is a view of a typical change in a transmitted signal used bythe modulation portion of FIG. 1;

FIG. 2B is a view of a frequency spectrum of a PSK-modulated signaloutput by a PSK modulator in the setup of FIG. 1;

FIG. 3A is a view of a typical change in a spread signal from a PNgenerator in the setup of FIG. 1;

FIG. 3B is a view of a frequency spectrum of a spread spectrum signaloutput by a spread spectrum modulator in the setup of FIG. 1;

FIG. 4 is a block diagram of a demodulating portion of a receiver foruse with the direct spread spectrum communication system of FIG. 1;

FIG. 5A is a view of a frequency spectrum of a signal used in the setupof FIG 4;

FIG. 5B is a view of a frequency spectrum of anther signal used in thesetup of FIG. 4;

FIG. 5C is a view of a frequency spectrum of another signal used in thesetup of FIG. 4;

FIG. 6A is a view of a frequency spectrum of another signal used in thesetup of FIG. 4;

FIG. 6B is a view of a frequency spectrum of another signal used in thesetup of FIG. 4;

FIG. 6C is a view of a frequency spectrum of another signal used in thesetup of FIG. 4;

FIG. 7 is a block diagram of a spread spectrum communication systempracticed as a first embodiment of the invention;

FIG. 8A is a view of a spectrum distribution pattern of a spreadspectrum signal used by the first embodiment wherein the amount oftraffic is normal;

FIG. 8B is a view of a spectrum distribution pattern of the spreadspectrum signal used by the first embodiment wherein the number ofcommunicating terminals is large;

FIG. 8C is a view of a spectrum distribution pattern of the spreadspectrum signal used by the first embodiment wherein the number ofcommunicating terminals is small;

FIG. 9 is a flowchart of steps in which the band width of the spreadspectrum signal and the clock rate are changed according to the amountof traffic in conjunction with the first embodiment;

FIG. 10 is a flowchart of steps in which the band width of the spreadspectrum signal and the clock rate are changed according to the S/Nratio of each terminal in conjunction with the first embodiment;

FIG. 11 is a block diagram of a base station constituting part of thefirst embodiment;

FIG. 12 is a block diagram of a terminal constituting part of the firstembodiment;

FIG. 13 is a block diagram of a typical modulator contained in the firstembodiment;

FIG. 14 is a block diagram of a mobile station practiced as a secondembodiment of the invention;

FIG. 15A is a view showing a relationship between clock rates andprocess gain in connection with the second embodiment;

FIG. 15B is a view showing another relationship between clock rates andprocess gain in connection with the second embodiment;

FIG. 16 is a view depicting a relationship between raised PN code clockrates and increased margins of power control precision in connectionwith the second embodiment;

FIG. 17 is a block diagram of a base station practiced as a thirdembodiment of the invention;

FIG. 18 is a block diagram of a mobile station practiced as a fourthembodiment of the invention;

FIG. 19 is a block diagram of a mobile station practiced as a fifthembodiment of the invention;

FIG. 20 is a view of a relationship between clock rates and process gainin connection with the fifth embodiment;

FIG. 21 is a view of a relationship between reduced transmitted signalspeeds and increased margins of power control precision in connectionwith the fifth embodiment;

FIG. 22 is a block diagram of a base station practiced as a sixthembodiment of the invention;

FIG. 23 is a block diagram of a mobile station practiced as a seventhembodiment of the invention;

FIG. 24 is a block diagram of a mobile station practiced as an eighthembodiment of the invention;

FIG. 25 is a block diagram of a mobile station practiced as a ninthembodiment of the invention;

FIG. 26 is a block diagram of a mobile station practiced as a tenthembodiment of the invention;

FIG. 27 is a block diagram of a mobile station practiced as an eleventhembodiment of the invention; and

FIG. 28 is a view of a relationship between bit error rates and per-bitreceiving power/interference power density ratios (Eb/No) in connectionwith the eleventh embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 7 is a block diagram of a spread spectrum communication systempracticed as the first embodiment of the invention. The figureschematically illustrates the basic concept of the first embodiment. Itis assumed that the first embodiment performs spread spectrumcommunication using the same pseudo noise (PN) code sequence as thatused by the prior art example.

In FIG. 7 a base station 1 of the spread spectrum communication systemis connected to a plurality (n) of terminals 2₁, 2₂, . . . , 2n. Thebase station 1 monitors the amount of its traffic to and from eachterminal while communicating therewith. When the number of communicatingterminals exceeds a predetermined threshold value, the process gain G isincreased, i.e., the band width of the spread spectrum signal is widenedin order to improve the S/N ratio. Conversely, if the number ofcommunicating terminals drops below a predetermined threshold value, theband width of the spread spectrum signal is reduced to the narrowestpossible width that permits communication. This lowers the clock ratefor reverse spread operation and thereby saves power.

FIG. 8A is a view of a spectrum distribution pattern of the spreadspectrum signal used by the first embodiment wherein the amount oftraffic is normal. The band width in this case is 2B_(A). FIG. 8B showsa spectrum distribution pattern of the spread spectrum signal used bythe first embodiment wherein the number of communicating terminals islarge. The band width in this case is 2B_(B). FIG. 8C depicts a spectrumdistribution pattern of the spread spectrum signal used by the firstembodiment wherein the number of communicating terminals is small. Theband width in this case is 2B_(c). The relationship among these bandwidths is defined as

B_(B) >B_(A) >B_(C)

The first embodiment may take on a case in which the base stationdetects the S/N ratio of the signal from each terminal within the samesystem and finds the overall ratio to have deteriorated. In that case,the base station may assume that a narrow band interference signal hasincreased due to a rise in the traffic of a totally different system,and may change the band width of the spread spectrum signal accordingly.For example, the climb in the mobile phone traffic in the morning andevening cause higher noise levels. When the increased noise is detected,the band width of the spread spectrum signal is widened and the processgain G is raised to prevent S/N ratio deterioration.

In any of the above cases where the band width of the spread spectrumsignal is changed, the base station instructs its terminals when tochange the band width, with what timing, and how much. In turn, theterminal station side is required to provide any one of a plurality ofappropriate clock rates for reverse spread operation on the spreadspectrum signal with its band width changed. The multiple clock ratesmay be generated in a number of ways, e.g., by division of a referenceclock rate or by switching of a plurality of oscillators.

FIG. 9 is a flowchart of steps in which the band width of the spreadspectrum signal and the clock rate are changed according to the amountof traffic in connection with the first embodiment, and FIG. 10 is aflowchart of steps in which the band width of the spread spectrum signaland the clock rate are changed according to the S/N ratio of eachterminal in conjunction with the first embodiment. Referring to FIG. 9,the base station detects the current amount of traffic T in step S11. Instep S12, the base station determines if the amount of traffic T isgreater than a predetermined threshold value T_(A). If the amount oftraffic T is found to be greater than the threshold value T_(A), stepS14 is reached; otherwise step S13 is reached. In step S14, the basestation instructs each terminal when to widen the band width and howmuch. More specifically, the base station transmits to each terminal asignal containing band width change instruction data. In turn, eachterminal in step S15 follows the instruction from the base station andswitches to an appropriate clock rate that permits reverse spreadoperation on the instructed band width.

In step S13, the base station checks to see if the currently detectedamount of traffic T is lower than another predetermined threshold valueT_(B) (T<T_(B), where T_(B) <T_(A)). If the amount of traffic T is foundto be lower than the threshold value T_(B), step S16 is reached. In stepS16, the base station instructs each terminal when to narrow the bandwidth of the spread spectrum signal and how much. Step S16 is followedby step S15 in which each terminal switches to an appropriate clock rateas instructed by the base station. If the amount of traffic T is foundto be equal to or greater than the threshold value T_(B), that means theamount of traffic T falls somewhere between the two threshold valueT_(A) and T_(B) (T_(B) ≦T≦T_(A)). In that case, step S13 is followed bystep S17 where the normal band width is maintained. If the terminalstation side at this point runs on a clock rate commensurate with awidened or narrowed band width, the clock rate corresponding to thenormal band width is now restored.

Alternatively, the S/N ratio of each terminal may be monitored for thepurpose of changing the band width of the spread spectrum signal and theclock rate in connection with the first embodiment, as indicated in theflowchart of FIG. 10. While steps S14 through S17 in FIG. 10 are thesame as in FIG. 9, steps S21 through S23 of FIG. 10 differ. Only thedifferent steps will be explained.

Referring to FIG. 10, the base station detects the S/N ratio x of thesignal from each terminal in step S21. The base station checks to see ifthe value x is smaller than a first threshold value x_(A) in step S22and if the value x is larger than a second threshold value X_(B) in stepS23. If the value x is found to be smaller than the first thresholdvalue x_(A) in step S22, step S14 is reached; otherwise step S23 isreached. If the value x is found to be larger than the second thresholdvalue x_(B) in step S23, step S16 is reached; otherwise step S17 isreached.

FIG. 11 is a block diagram of atypical base station constituting part ofthe first embodiment, and FIG. 12 is a block diagram of a typicalterminal also constituting part of the first embodiment. At the basestation side, as shown in FIG. 11, a transmitted signal from eachterminal is received by a receiving antenna 31. The received signal,which is a radio frequency (RF) signal, is forwarded to a frequencyconversion circuit 32 for conversion to an intermediate frequency (IF)signal. If the base station is a digital processing setup, the frequencyconversion circuit 32 also performs A/D conversion. The converted signalis sent to a plurality of demodulating blocks 33₁, 33₂, . . . , 33n. Thenumber of the demodulating blocks in the base station varies with theexpected amount of traffic. Each of the demodulating blocks 33₁, 33₂, .. . , 33n performs reverse spread operation using the PN code sequencefrom a pseudo noise (PN) generation circuit 38 and then carries-out datademodulation. If the transmitted data are in coded format, they aredecoded by the demodulating blocks. The demodulated data are forwardedto a data processing and control circuit 34 (e.g., base band processor).The data processing and control circuit 34 processes the data received,controls data transmission and reception, and controls the switching toan appropriate clock rate for the pseudo noise (PN).

The base station transmits data to each of its terminals as follows: Thedata processing and control circuit 34 sends necessary data tomodulating blocks 35₁, 35₂, . . . , 35n for modulation and coding. Themodulating blocks modulate and code the data received before subjectingthem to spread spectrum processing using the PN code from a pseudo noise(PN) generation circuit 39. The processed data signal is convertedthrough amplification by a high-power amplifier 36 to a transmissionoutput signal. The amplified signal is broadcast by radio from atransmitting antenna 47 to each of the terminals. With this embodiment,the base station has its data processing and control circuit 34 monitorthe amount of traffic T illustratively by counting the number of activecircuits in the demodulating blocks 33₁, 33₂, etc. Then the clock rateof the pseudo noise (PN) code sequence is changed as needed for reversespread operation by the demodulating blocks 33₁, 33₂, etc. or for spreadspectrum operation by the modulating blocks 35₁, 35₂, etc.

Where the S/N ratio of the signal from each terminal is monitored forclock rate control, the demodulating blocks 33₁, 33₂, etc. initiallydetect the S/N ratio of the signal received. The detected signal is sentto the data processing and control circuit 34 (e.g., base bandprocessor). Based on the signal it received, the circuit 34 changes theclock rate of the PN code for reverse spread operation or for spreadspectrum operation.

Similar processing also takes place on the terminal station side, asillustrated in FIG. 12. Referring to FIG. 12, a radio frequency (RE)signal received by a receiving antenna 41 is forwarded to a frequencyconversion circuit 42 for conversion to an intermediate frequency (IF)signal. A demodulating block 43 demodulates the signal received from thecircuit 42 and carries out reverse spread operation using the PN codeThe processed signal is fed to a data processing and control circuit 44(e.g., base band processor) for data processing and control overtransmission and reception. The data from the circuit 44 is sent to amodulating block 45 for modulation and PN coding. The output of themodulating block 45 is converted (i.e., amplified) by a high-poweramplifier 46 into a signal ready for transmission. This signal istransmitted via a transmitting antenna 47 to the base station. At theterminal station side, the data processing and control circuit 44changes the clock rate of the PN code for the reverse spread operationby the demodulating block 43 and for the spread spectrum operation bythe modulating block 45 in accordance with the clock changeoverinstruction signal from the base station.

FIG. 13 is a block diagram of a typical modulator representative of themodulating blocks 35₁, 35₂, etc. and 45. In the setup of FIG. 13,incoming data are subjected to BPSK (bi-phase shift keying) before beingconverted to a spread spectrum signal.

Referring to FIG. 13, incoming data from the data processing and controlcircuit 34 (or 44) are sent to a multiplier 53 via an input terminal 51.The multiplier 53 multiplies the data by a carrier signal from anotherinput terminal 52 to generate a BPSK-modulated signal. TheBPSK-modulated signal is forwarded to a multiplier 57. In turn, themultiplier 57 multiplies the BPSK-modulated signal by the PN codegenerated by a PN code generator 54, thereby generating a spreadspectrum signal. This signal is output from an output terminal 58. Inthis embodiment, the PN code generator is supplied with one of the clocksignals generated by a plurality of clock generators 56₁, 56₂, etc. Theclock signal to the PN code generator is selected by a changeover switch55. The changeover switch 55 is controlled by the data processing andcontrol circuit 34 detecting the amount of traffic or like parameter andsending a signal reflecting that parameter to a control terminal 59. Onthe terminal station side, the data processing and control circuit 44supplies the control terminal 59 with a control signal that containsclock rate change instruction data. Needless to say, the base stationand any of its terminals communicating therewith must select the sameclock rate for their spread spectrum and reverse spread operations.

As described, the first embodiment controls the band width of the spreadspectrum signal in accordance with the amount of traffic between thebase station and its terminals. When the amount of traffic is high,deterioration of the S/N ratio is prevented; when the amount of trafficis low, power dissipation is reduced.

FIG. 14 is a block diagram of a mobile station practiced as the secondembodiment of the invention. In FIG. 14, an input terminal, not shown,of the mobile station is fed with a transmitted signal dT(t) such as adigital audio signal. The transmitted signal dT(t) is forwarded to aclock rate change information combining unit 101. When it is necessaryto change the clock rate of a transmission spread code, the clock ratechange information combining unit 101 combines the transmitted signaldT(t) with clock rate change information.

The signal output by the clock rate change information combining unit101 is sent to an encoder 102 for coding in error correcting code. Thecoded signal from the encoder 102 is forwarded to a PSK (phase shiftkeying) modulator 103 which is fed with a carrier fc from a carriergenerator, not shown. The PSK modulator 103 subjects the carrier fc tobi-phase shift keying (BPSK) using the signal received.

The PSK-modulated signal from the PSK modulator 103 is supplied to aspread spectrum modulator 104 which is also fed with a spread code p(t).Using the spread code p(t), the spread spectrum modulator 104 puts thePSK-modulated signal to spread spectrum modulation. The spread spectrumsignal from the spread spectrum modulator 104 has its center frequencyconverted to a high frequency by a frequency converter 107. Theresulting signal from the frequency converter 107 passes through anoutput (high-power) amplifier 108 and an antenna sharing unit 109. Goingpast the antenna sharing unit 109, the signal reaches atransmitting-receiving antenna 110 which transmits the signal to thebase station.

The spread spectrum signal from the base station is received by thetransmitting-receiving antenna 110. From the antenna 110, thesignal-passes through the antenna sharing unit 109 and a low-noiseamplifier 111 to reach a frequency converter 112. The frequencyconverter 112 converts the center frequency of the received signal tothe operating frequency of a demodulator 113. The spread spectrum signalfrom the frequency converter 112 is fed to the demodulator 113 forreverse spread operation and PSK demodulation.

The signal from the demodulator 113, coded in error correcting code, iscorrected for error by a decoder 114 and sent to a receiving portiondownstream. The input and the output signals to and from the decoder 114are supplied to a bit error rate (BER) detector 115 for BER calculationand evaluation. Near the upper limit of the system's line capacity, thebit error rate of the received signal from the mobile station can exceeda threshold value of about 3.0×10.

If the BER detector 115 finds that the threshold value of 3.0×10 isexceeded, the detector 115 causes the transmission spread code clockgenerator 106 to raise the clock rate of the spread code included in thetransmitted signal.

In the second embodiment, as described, the BER detector 115 causes thetransmission spread code clock generator 106 to raise the clock rate ofthe transmission spread code where the transmission quality of thereceived signal degenerates near the upper limit of the system's linecapacity. With the transmission spread code clock rate increased in thevicinity of the tipper limit of the system's line capacity, the periodTp of the change in the transmission spread code p(t) is shortened andthe process gain of spread spectrum processing is enhanced. Thisprovides greater margins of power control precision

FIG. 15A is a view showing a relationship between clock rates andprocess pain in connection with the second embodiment, and FIG. 15B is aview showing another relationship between clock rates and process gainin connection with the second embodiment. In the figures, the processgain is denoted by G, and the data rate of the transmitted signal by Bd(signal period: Td) In the case of FIG. 15A where the clock rate of thespread code is (period: T₁), G=B₁ /Bd. In the case of FIG. 15B where theclock rate of the spread code is B₂ (period: T₂), G=B₂ /Bd. Raising thespread code clock rate from B₁ to B₂ spreads the signal over a widerband width and improves the process gain by B₂ /B₁.

FIG. 16 is a view depicting a relationship between raised transmissionspread code clock rates and increased margins of power control precisionin connection with the second embodiment. As illustrated, raising thetransmission spread code clock rate-near the upper limit of the system'sline capacity provides the output high-power amplifier 108 withsignificantly greater margins of power control precision.

The theory of spread spectrum communication dictates that at least apower control precision level of 0.5 dB is required in order to maintainabout 90 percent of the system's theoretical line capacity. Multiplyingthe clock rate of the spread code by, say, 1.2 provides an extra marginof 0.8 dB. This means that the line capacity is maintained at a powercontrol precision level of 1.3 dB. The increased margin of power controlprecision translates into a much simpler construction of the powercontrol circuit in the transmitting portion of the mobile station.

Because the process gain is raised by increasing the clock rate of thetransmission spread code, the gain of the output amplifier 108 may bereduced under control of the BER detector 115 to the lowest practicablelevel as long as the minimum bit error rate is not exceeded. Thisarrangement reduces power dissipation.

FIG. 17 is a block diagram of a base station practiced as the thirdembodiment of the invention, and FIG. 18 is a block diagram of a mobilestation practiced as the fourth embodiment of the invention. Referringto FIG. 17, a spread spectrum signal from a mobile station enters atransmitting-receiving antenna 130, passes through an antenna sharingunit 129 and a low-noise amplifier 131, and reaches a frequencyconverter 132. The frequency converter 132 converts the center frequencyof the spread spectrum signal to the operating frequency of ademodulator 133. The spread spectrum signal output by the frequencyconverter 132 passes through a band-pass filter 136 and arrives at thedemodulator 133. The demodulator 133 puts the signal received to reversespread operation and PSK demodulation.

The signal from the demodulator 133, coded in error correcting code, iscorrected for error by a decoder 134 and sent to a receiving portiondownstream. The input and the output signals to and from the decoder 134are supplied to a bit error rate (BER) detector 135 for BER calculationand evaluation. Near the upper limit of the system's line capacity, thebit error rate of the received signal from the mobile station can exceeda threshold value of about 3.0×10.

A mobile station spread code clock rate control information generator137 generates and outputs clock rate control information for controllingthe clock rate of the mobile station transmission spread code. If theBER detector 135 finds that the threshold value of about 3.0×10 isexceeded, the detector 135 causes the generator 137 to generate clockrate control information for raising the mobile station transmissionspread code clock rate. At this point, the clock rate controlinformation generator 137 causes the band-pass filter 136 to switch itspass band width to the clock rate designated by the control informationin preparation for the next mobile station transmission.

Referring to FIG. 17, a transmitted signal dT(t) such as a digital audiosignal is first fed to a clock rate control information combining unit121. The combining unit 121 combines the transmitted signal dT(t) withthe mobile station transmission spread code control informationgenerated by the clock rate control information generator 137. Thetransmitted signal output by the combining unit 121 is coded in errorcorrecting code by an encoder 122. The coded signal is sent to a PSKmodulator 123 which is fed with a carrier fc from a carrier generator,not shown. The PSK modulator 123 subjects the carrier fc to bi-phaseshift keying using the signal received.

The PSK-modulated signal from the PSK modulator 123 is supplied to aspread spectrum modulator 124 which is also fed with a spread code p(t).Using the spread code p(t), the spread spectrum modulator 124 puts thePSK-modulated signal to spread spectrum modulation. The spread spectrumsignal from the spread spectrum modulator 124 has its center frequencyconverted to a high frequency by a frequency converter 127. Theresulting signal from the frequency converter 127 passes through anoutput (high-power) amplifier 128 and an antenna sharing unit 129. Goingpast the antenna sharing unit 129, the signal reaches atransmitting-receiving antenna 130 which transmits the signal to themobile station.

As mentioned, FIG. 18 is a block diagram of a mobile station practicedas the fourth embodiment of the invention. In the fourth embodiment, theparts that are functionally identical to those already described inconnection with the second embodiment of FIG. 14 are designated by thesame reference numerals, and repetitive descriptions thereof areabbreviated. In the fourth embodiment, the signal received from the basestation is processed in the same manner as in the second embodiment tipto the decoder 114. The decoder 114 outputs the received signal combinedwith mobile station transmission spread code clock rate controlinformation. This signal is fed to a clock rate control informationextracting unit 116. The extracting unit 116 rids the signal received ofits clock rate control information and forwards the resulting signaldR(t) to a receiving portion downstream.

The clock rate control information extracted by the extracting unit 116is supplied to the spread code clock generator 106 for control overtransmission spread code clock rates. The constructions and functions ofthe other parts in the fourth embodiment of FIG. 18 are the same as inthe second embodiment of FIG. 14.

The fourth embodiment of the above constitution works as follows: Thebase station generates clock rate control information for raising theclock rate of the mobile station transmission spread code as per theoutput of the BER detector 135 where the transmission quality of thereceived signal of the base station degenerates near the upper limit ofthe system's line capacity. The clock rate control information is thuscombined with the transmitted signal dT(t) and transmitted to the mobilestation. Upon receipt of the signal, the mobile station raises the clockrate of the transmission spread code from the transmission spread codeclock generator 106 in accordance with the clock rate controlinformation extracted by the clock rate control information extractingunit 116. When the base station receives from the mobile station thesignal with its spread code clock rate changed, the band width of theband-pass filter 136 is made to match the mobile station transmissionspread code clock rate under control of the clock rate controlinformation generator 137. Thus the demodulator 133 performs reversespread operation and demodulation appropriately.

The above-described workings of control shorten the period Tp of thechange in the transmission spread code p(t) in the vicinity of the upperlimit of the system's line capacity, enhance the process gain of spreadspectrum operation and increase margins of power control precision. Itfollows that, as in the case of the second embodiment in FIG. 14, thefourth embodiment allows the power control circuit of the mobile stationto be appreciably simplified in construction.

The fourth embodiment is not limitative of the invention. A modificationof the embodiment may involve reducing the gain of the output amplifier108 to the lowest practicable level as long as the minimum bit errorrate (BER) is not exceeded, because the process gain is increased byraising the transmission spread code clock rate. This modificationreduces power dissipation. Another modification of the fourth embodimentmay be to determine the transmission quality of the signal using an S/Nratio detection circuit instead of the BER detection arrangement. Afurther modification may be to utilize QPSK or any other suitablemodulation method in place of the bi-phase shift keying (BPSK)modulation.

FIG. 19 is a block diagram of a mobile station practiced as the fifthembodiment of the invention. The fifth embodiment operates inapplications of spread spectrum communication between base station andmobile station. Referring to FIG. 19, a transmitted signal d(t) such asan analog audio signal is first fed to a binary modulator 301. Thetransmitted signal d(t) output by the binary modulator 301 is a binarycoded signal. The period Td of the transmitted signal d(t) is determinedby the transmission clock rate of a transmission clock generator 302.

The transmitted signal d(t) from the binary modulator 301 is coded inerror correcting code by an encoder 303. The coded signal is sent to aPSK modulator 304 which is fed with a carrier fc from a carriergenerator, not shown. The PSK modulator 304 subjects the carrier fc tobi-phase shift keying using the transmitted signal d(t).

The PSK-modulated signal from the PSK modulator 304 is supplied to aspread spectrum modulator 305 which is also fed with a spread signalp(t). Using the spread signal p(t), the spread spectrum modulator 305puts the PSK-modulated signal to spread spectrum modulation.

The spread spectrum signal from the spread spectrum modulator 305 hasits center frequency converted to a high frequency by an upwardconverter 306. The resulting signal from the upward converter 306 issent via an output (high-power) amplifier 307 to atransmitting-receiving antenna 308. The antenna 308 transmits the signalto the base station.

The spread spectrum signal from the base station is admitted through thetransmitting-receiving antenna 308 and fed to a downward converter 309.The downward converter 309 converts the center frequency of the spreadspectrum signal to the same frequency as that of the carrier fc. Thespread spectrum signal from the downward converter 309 is supplied to ademodulator 310 for spread spectrum demodulation and PSK demodulation.

The demodulator 310 outputs the signal d(t) coded in error correctingcode. The coded signal is corrected for error by a decoder 311 beforebeing sent to a receiving portion downstream. The input and outputsignals to and from the decoder 311 are fed to a bit error rate (BER)detector 312 for BER calculation and evaluation. In the vicinity of thetipper limit of the system's line capacity, the bit error rate of thereceived signal of the mobile station can exceed a threshold value ofabout 3.0×10⁻³. If the BER detector 312 finds that the bit rate errorexceeds the threshold value of 3.0×10⁻³, the BER detector 312 causes thetransmission clock generator 302 to reduce the transmission clock rate.

In the fifth embodiment of the above constitution, as described, the BERdetector 312 causes the transmission clock generator 302 to reduce thetransmission clock rate where the transmission quality of the receivedsignal degenerates near the upper limit of the system's line capacity.This prolongs the period Td of the transmitted signal d(t) near theupper limit of the system's line capacity, thereby improving the processgain of spread spectrum operation and increasing the margins of powercontrol precision.

FIG. 20 is a view of a relationship between clock rates and process gainin connection with the fifth embodiment. If the process gain is denotedby Gp, then Gp=B/B₁ for characteristic (1) in the figure, and Gp=B/B₂for characteristic (2) . Lowering the clock rate from T₁ to T₂ sharpensthe frequency spectrum characteristic and thereby improves the processgain by B₁ /B₂.

FIG. 21 is a view of a relationship between reduced transmitted signalspeeds and increased margins of power control precision in connectionwith the fifth embodiment. As described, lowering the clock rate nearthe upper limit of the system's line capacity supplements the controlprecision of the output amplifier 307 with the extra margins shown inFIG. 21.

The highest precision level theoretically required of the spreadspectrum communication method is within 0.5 dB, as mentioned earlier.Lowering the clock rate by, say, 10 percent provides an extra margin of0.5 dB in terms of power control precision. That is, the most stringentprecision requirement is met with a power control precision margin of1.0 dB. This means that the precision requirement for the mobile stationmay be much less rigorous than before where the fifth embodiment isemployed.

Lowering the clock rate of the transmitted signal increases the energyof that signal. Given the signal energy increase, the gain of the outputamplifier 307 may be reduced to the lowest practicable level undercontrol of the BER detector 312 as long as the bit error rate does notdeteriorate. This reduces power dissipation.

FIG. 22 is a block diagram of a base station practiced as the sixthembodiment of the invention, and FIG. 23 is a block diagram of a mobilestation practiced as the seventh embodiment of the invention. Referringto FIG. 22, a spread spectrum signal From a mobile station is admittedthrough a transmitting-receiving antenna 321 into a downward converter322. The downward converter 322 converts the center frequency of thereceived signal to the same frequency as that of the carrier fc.

The spread spectrum signal output by the downward converter 322 is fedto a demodulator 323 for spread spectrum demodulation and PSKdemodulation. The demodulator 323 outputs a signal d(t) coded in errorcorrecting code. The coded signal d(t) is corrected for error by adecoder 324 before being sent to a receiving portion downstream.

The input and output signals to and from the decoder 324 are supplied toa bit error rate (BER) detector 325 for BER calculation and evaluation.In the vicinity of the upper limit of the system's line capacity, thebit error rate of the received signal from the mobile station can exceeda threshold value of about 3.0×10⁻¹.

A clock rate control information generator 326 generates and outputsclock rate control information for controlling the transmission clockrate of the mobile station. If the BER detector 326 finds that the biterror rate exceeds the threshold value of 3.0×10⁻³, the BER detector 325causes the generator 326 to generate clock rate control information forreducing the transmission clock rate.

The transmitted signal d(t) such as an analog audio signal is suppliedto a binary modulator 327. In turn, the binary modulator 327 outputs thetransmitted signal d(t) as a binary coded signal. The period Td of thetransmitted signal d(t) is determined according to the transmissionclock rate provided by a transmission clock generator 328.

The transmitted signal d(t) output by the binary modulator 327 is sentto a clock rate control information combining unit 29. The combiningunit 29 combines the transmitted signal d(t) with the clock rate controlinformation generated by the clock rate control information generator326.

The transmitted signal d(t) combined with the clock rate controlinformation from the combining unit 329 is coded in error correctingcode by an encoder 330. The coded signal is forwarded to a PSK modulator331 which is fed with the carrier fc from a carrier generator, notshown. The PSK modulator 331 subjects the carrier fc to bi-phase shiftkeying using the transmitted signal d(t)

The PSK-modulated signal from the PSK modulator 331 is supplied to aspread spectrum modulator 332. The spread spectrum modulator 332 is alsofed with the spread signal p(t). Using the spread signal p(t), thespread spectrum modulator 332 subjects the PSK-modulated signal tospread spectrum modulation.

The spread spectrum signal output by the spread spectrum modulator 332has its center frequency converted to a high frequency by an upwardconverter 333. The converted signal from the upward converter 333 issent via an output amplifier (high-power amplifier) 334 to thetransmitting-receiving antenna 321. The antenna 321 transmits the signalto the mobile station.

FIG. 23 is a block diagram of a mobile station practiced as the seventhembodiment of the invention. In the seventh embodiment of FIG. 23, theparts that are functionally identical to those already described inconnection with the fifth embodiment of FIG. 19 are designated by thesame reference numerals, and repetitive descriptions thereof areabbreviated.

Referring to FIG. 23, the signal d(t) output by a decoder 311 andcombined with clock rate control information is sent to a clock ratecontrol information extracting unit 313. The extracting unit 313 ridsthe signal received of its clock rate control information and forwardsthe resulting signal d(t) to a receiving portion downstream. The clockrate control information extracted by the extracting unit 313 is fed toa transmission clock generator 302 for control over transmission clockrates. The constructions and functions of the other parts in the seventhembodiment of FIG. 23 are the same as in the fifth embodiment of FIG.19.

The seventh embodiment of the above constitution works as follows: Thegenerator 326 of the base station generates clock rate controlinformation for raising the clock rate of the transmitted signal wherethe transmission quality of the received signal of the base stationdegenerates near the upper limit of the system's line capacity. Theclock rate control information is combined with the transmitted signald(t) and transmitted to the mobile station. The clock rate controlsinformation extracted by the extracting unit 313 of the mobile stationlowers the rate of the transmission clock from the transmission clockgenerator 302. As a result, the period Id of the change in thetransmitted signal d(t) is prolonged near the upper limit of thesystem's line capacity. This affords greater margins of power controlprecision to the power control circuit and contributes to making theprecision requirement of the mobile station more lenient, as with thefifth embodiment of FIG. 19.

Lowering the clock rate of the transmitted signal raises the energy ofthat signal. Given the signal energy increase, the gain of the outputamplifier 307 may be reduced to the lowest practicable level accordingto the clock rate control information detected by the extracting unit313 as long as the bit error rate does not deteriorate. This reducespower dissipation.

The seventh embodiment determines the transmission quality of the signalby detecting the bit error rate thereof. Alternatively, the transmissionquality may be determined by use of an S/N ratio detection circuit.Another alternative is to detect the amount of traffic instead oftransmission quality for control purposes.

FIG. 24 is a block diagram of a mobile station practiced as the eighthembodiment of the invention. The embodiment involves applying theinvention to a mobile station for SS-CDMA communications where the basestation maintains the same level of transmitting power on alltransmitting channels In such cases, the transmitting power level servesas the reference for signal intensity

Referring to FIG. 24, a spread spectrum signal (composite signal of thesignals on all channels) output by a downward converter 407 is sent viaa distributor to a demodulator 408. The spread spectrum signaldistributed by the distributor 411 is also fed to a level detectioncircuit 412. The level detection circuit 412 detects the level of thereceived signal.

A control circuit 413 compares the transmitting power of the basestation with that level of the received signal which is detected by thelevel detection circuit 412. The comparison allows the circuit 413 toestimate power losses over propagation paths. Accordingly the controlcircuit 413 adjusts the gain of an output amplifier 405 to control thetransmitting power so that the base station will maintain an appropriatereceived signal level. This transmitting power control operation iscarried out repeatedly.

The eighth embodiment keeps the transmitting power at the appropriatelevel all the time. This means that the mobile station can communicatewith the base station at the appropriate transmitting power level fromthe first transmission onward. Because of its ability to receive signalsat the appropriate level from the start, the base station ensures stableand unfailing communications. Since the mobile station can transmit itssignal always at the appropriate power level, the power consumption ofthe mobile station is reduced. This leads to a smaller size and a longerlife of the batteries incorporated in the mobile station. With itssignal always transmitted at the appropriate power level, the mobilestation avoids interference with other communications. For SS-CDMAcommunications that are particularly vulnerable to interference waves,the eighth embodiment allows the system's line capacity to be set closeto its theoretical upper limit.

FIG. 25 is a block diagram of a mobile station practiced as the ninthembodiment of the invention. As illustrated in the figure, the ninthembodiment, besides operating on the control method described above, isalso capable of controlling the transmitting power by use of a powercontrol signal Spc superimposed on a traffic channel and transmittedfrom the base station. The additional Spc-based transmitting powercontrol method may be used for fine power adjustment while theabove-described method is used for coarse adjustment.

FIG. 26 is a block diagram of a mobile station practiced as the tenthembodiment of the invention, and FIG. 27 is a block diagram of a mobilestation practiced as the eleventh embodiment of the invention. Theseembodiments involve applying the invention to mobile stations forSS-CDMA communications where the base station transmits informationabout its total transmitting power over a control channel. Thatinformation serves as the reference for the intensity of transmittingpower

Referring to FIG. 26, a spread spectrum signal output by a downwardconverter 407 is sent via an AGC amplifier 408a to a demodulator 408b.The demodulator 408b subjects the signal received to spread spectrumdemodulation and PSK demodulation. The output signal of the demodulator408b is fed to a decoder 409. The output signal of the demodulator 408bis also supplied to an AGC control circuit 408c. The control circuit408c controls the gain of the AGC amplifier 408a so that the outputlevel of the demodulator 408b will reach a predetermined value. In thatcase, the control signal sent from the AGC control circuit 408c to theAGC amplifier 408a corresponds to the signal power of the receivingchannel. This allows the AGC control circuit 408c to measure the signalpower of the receiving channel. The result of the measurement is sent toa control circuit 414.

The control circuit 414 compares the result of signal power measurementson the receiving channel with the transmitting power information decodedby the decoder 409. The comparison allows the control circuit 414 toestimate power losses over propagation paths. Accordingly, the controlcircuit 414 adjusts the gain of an output amplifier 405 to control thetransmitting power so that the base station will maintain an appropriatereceived signal level. This transmitting power control operation iscarried out repeatedly.

Referring now to FIG. 27, the input to and the output from a decoder 409are detected by a bit error rate (BER) detection circuit 415. The BERdetection circuit 415 detects a bit error rate from the data received,and supplies the detected bit error rate to a control circuit 416.

The control circuit 416 obtains the value of Eb/No from the received biterror rate and acquires the power level of the received signal fromEb/No, where Eb stands for the receiving power per bit and No for thepower density of interference waves. FIG. 28 is a view of a relationshipbetween bit error rates and per-bit receiving power/interference powerdensity ratios (Eb/No) in connection with the eleventh embodimentoperating on CDMA.

The control circuit 416 compares the received signal power with thetransmitting power information supplied by the decoder 409. Thecomparison allows the control circuit 416 to estimate power losses overpropagation paths. Accordingly, the control circuit 416 adjusts the gainof an output amplifier 405 to control the transmitting power so that thebase station will maintain an appropriate received signal level Thistransmitting power control operation is carried out repeatedly.

When the receiving channel is switched from the control channel to thetraffic channel (i.e., communication channel) in any one of the tenthembodiment of FIG. 26 and the eleventh embodiment of FIG. 27, thetransmitting power information from the base station, if found thetraffic channel, may be utilized to continue control over thetransmitting power at the mobile station side. Thus with thetransmitting power always held at the appropriate level, the tenth andthe eleventh embodiments provide the same benefits as those of theforegoing embodiments.

The tenth and the eleventh embodiments of FIGS. 26 and 27, besidesoperating on the control method described above, are also capable ofcontrolling the transmitting power by use of a power control signal Spcsuperimposed on the traffic channel and transmitted from the basestation, as depicted in FIG. 25. The additional Spc-based transmittingpower control method may be used for fine power adjustment while theabove-described method is used for coarse adjustment.

It is to be understood that while the invention has been described inconjunction with specific embodiments, it is evident that manyalternatives, modifications and variations will become apparent to thoseskilled in the art in light of the foregoing description. Accordingly,it is intended that the present invention embrace all such alternatives,modifications and variations as fall within the spirit and scope of theappended claims.

What is claimed is:
 1. A spread spectrum communication system forperforming spread spectrum communication by superimposing a pseudo noisesignal on a transmitted signal, said spread spectrum communicationsystem comprising:transmission quality determining means for determiningthe transmission quality of a received signal; and means for changingthe clock frequency of said pseudo noise signal in accordance with saidtransmission quality determined by said transmission quality determiningmeans; wherein said transmission quality determining means includessignal-to-noise ratio detecting means for addressing said receivedsignal.
 2. A spread spectrum transmitter-receiver for superimposing apseudo noise signal on a transmitted signal and for receiving saidtransmitted signal containing the superimposed pseudo noise signal, saidspread spectrum transmitter-receiver comprising:transmission qualitydetermining means for determining the transmission quality of a receivedsignal; means for controlling the clock rate of said pseudo noise signalin accordance with said transmission quality determined by saidtransmission quality determining means; and means for combininginformation about the changed clock rate with said transmitted signal,wherein said transmission quality determining means includessignal-to-noise ratio detecting means for addressing said receivedsignal.
 3. A spread spectrum transmitter-receivercomprising:transmission quality determining means for determining thequality of a received signal from the other spread spectrumtransmitter-receiver; control data generating means for generating clockcontrol data for controlling the clock rate of a pseudo noise signalfrom said other spread spectrum transmitter-receiver in accordance withsaid transmission quality determined by said transmission qualitydetermining means; data combining means for combining with a transmittedsignal said clock control data generated by said control data generatingmeans; and a band-pass filter circuit for controlling a passing band inaccordance with the changed clock rate of said pseudo noise signal insaid received signal from said other spread spectrumtransmitter-receiver, wherein said transmission quality determiningmeans includes signal-to-noise ratio detecting means for addressing saidreceived signal.
 4. A spread spectrum transmitter-receiver according toclaim 3, further comprising:data extracting means for extracting saidclock control data from said received signal coming from said otherspread spectrum transmitter-receiver; and clock control means forcontrolling the clock rate of said pseudo noise signal in accordancewith said clock control data extracted by said data extracting means. 5.A spread spectrum transmitter-receiver system comprising:a second spreadspectrum transmitter-receiver having transmission quality determiningmeans for determining the transmission quality of a received signal froma first spread spectrum transmitter-receiver, control data generatingmeans for generating clock control data for controlling the clock rateof a pseudo noise signal from said first spread spectrumtransmitter-receiver in accordance with said transmission qualitydetermined by said transmission quality determining means, and datacombining means for combining with a transmitted signal said clockcontrol data generated by said control data generating means; and saidfirst spread spectrum transmitter-receiver having data extracting meansfor extracting said clock control data from a received signal from saidsecond spread spectrum transmitter-receiver, and clock control means forcontrolling the clock rate of said pseudo noise signal in accordancewith said clock control data extracted by said data extracting means,wherein said transmission quality determining means includessignal-to-noise ratio detecting means for addressing said receivedsignal.
 6. A spread spectrum communication system for performing spreadspectrum communication by superimposing a pseudo noise signal on atransmitted signal, said spread spectrum communication systemcomprising:transmission quality determining means for determining thetransmission quality of a received signal; and means for changing theclock frequency of said transmitted signal in accordance with saidtransmission quality determined by said transmission quality determiningmeans, wherein said transmission quality determining means includessignal-to-noise ratio detecting means for addressing said receivedsignal.
 7. A spread spectrum transmitter-receiver for superimposing apseudo noise signal on a transmitted signal and for receiving saidtransmitted signal containing the superimposed pseudo noise signal, saidspread spectrum transmitter-receiver comprising:transmission qualitydetermining means for determining the transmission quality of a receivedsignal; means for controlling the clock rate of said transmitted signalin accordance with said transmission quality determined by saidtransmission quality determining means; and means for combininginformation about the changed clock rate with said transmitted signal,wherein said transmission quality determining means includessignal-to-noise ratio detecting means for addressing said receivedsignal.
 8. A spread spectrum transmitter-receiver system comprising:afirst spread spectrum transmitter-receiver having transmission qualitydetermining means for determining the transmission quality of a receivedsignal, control data generating means for generating clock control datafor controlling the clock rate of a transmitted signal in accordancewith said transmission quality determined by said transmission qualitydetermining means, and data combining means for combining with saidtransmitted signal said clock control data generated by said controldata generating means; and a second spread spectrum transmitter-receiverhaving data extracting means for extracting said clock control data fromsaid received signal, and clock control means for controlling the clockrate of said transmitted signal in accordance with said clock controldata extracted by said data extracting means, wherein said transmissionquality determining means includes signal-to-noise ratio detecting meansfor addressing said received signal.
 9. A spread spectrum communicationsystem for performing spread spectrum communication by superimposing apseudo noise signal on a transmitted signal, said spread spectrumcommunication system comprising:transmission quality determining meansfor determining the transmission quality of a received signal; and meansfor changing the clock frequency of said pseudo noise signal inaccordance with said transmission quality determined by saidtransmission quality determining means, wherein said transmissionquality determining means includes bit error rate detecting means foraddressing said received signal.
 10. A spread spectrumtransmitter-receiver for superimposing a pseudo noise signal on atransmitted signal and for receiving said transmitted signal containingthe superimposed pseudo noise signal, said spread spectrumtransmitter-receiver comprising:transmission quality determining meansfor determining the transmission quality of a received signal; means forcontrolling the clock rate of said pseudo noise signal in accordancewith said transmission quality determined by said transmission qualitydetermining means; and means for combining information about the changedclock rate with said transmitted signal, wherein said transmissionquality determining means includes bit error rate detecting means foraddressing said received signal.
 11. A spread spectrumtransmitter-receiver comprising:transmission quality determining meansfor determining the quality of a received signal from the other spreadspectrum transmitter-receiver; control data generating means forgenerating clock control data for controlling the clock rate of a pseudonoise signal from said other spread spectrum transmitter-receiver inaccordance with said transmission quality determined by saidtransmission quality determining means; data combining means forcombining with a transmitted signal said clock control data generated bysaid control data generating means; and a band-pass filter circuit forcontrolling a passing band in accordance with the changed clock rate ofsaid pseudo noise signal in said received signal from said other spreadspectrum transmitter-receiver, wherein said transmission qualitydetermining means includes bit error rate detecting means for addressingsaid received signal.
 12. A spread spectrum transmitter-receiver systemcomprising:a second spread spectrum transmitter-receiver havingtransmission quality determining means for determining the transmissionquality of a received signal from a first spread spectrumtransmitter-receiver, control data generating means for generating clockcontrol data for controlling the clock rate of a pseudo noise signalfrom said first spread spectrum transmitter-receiver in accordance withsaid transmission quality determined by said transmission qualitydetermining means, and data combining means for combining with atransmitted signal said clock control data generated by said controldata generating means; and said first spread spectrumtransmitter-receiver having data extracting means for extracting saidclock control data from a received signal from said second spreadspectrum transmitter-receiver, and clock control means for controllingthe clock rate of said pseudo noise signal in accordance with said clockcontrol data extracted by said data extracting means, wherein saidtransmission quality determining means includes bit error rate detectingmeans for addressing said received signal.
 13. A spread spectrumcommunication system for performing spread spectrum communication bysuperimposing a pseudo noise signal on a transmitted signal, said spreadspectrum communication system comprising:transmission qualitydetermining means for determining the transmission quality of a receivedsignal; and means for changing the clock frequency of said transmittedsignal in accordance with said transmission quality determined by saidtransmission quality determining means, wherein said transmissionquality determining means includes bit error rate detecting means foraddressing said received signal.
 14. A spread spectrumtransmitter-receiver for superimposing a pseudo noise signal on atransmitted signal and for receiving said transmitted signal containingthe superimposed pseudo noise signal, said spread spectrumtransmitter-receiver comprising:transmission quality determining meansfor determining the transmission quality of a received signal; means forcontrolling the clock rate of said transmitted signal in accordance withsaid transmission quality determined by said transmission qualitydetermining means; and means for combining information about the changedclock rate with said transmitted signal, wherein said transmissionquality determining means includes bit error rate detecting means foraddressing said received signal.
 15. A spread spectrumtransmitter-receiver system comprising:a first spread spectrumtransmitter-receiver having transmission quality determining means fordetermining the transmission quality of a received signal, control datagenerating means for generating clock control data for controlling theclock rate of a transmitted signal in accordance with said transmissionquality determined by said transmission quality determining means, anddata combining means for combining with said transmitted signal saidclock control data generated by said control data generating means; anda second spread spectrum transmitter-receiver having data extractingmeans for extracting said clock control data from said received signal,and clock control means for controlling the clock rate of saidtransmitted signal in accordance with said clock control data extractedby said data extracting means, wherein said transmission qualitydetermining means includes bit error rate detecting means for addressingsaid received signal.